The synthesis and assembly of microtubules during flagellar regeneration in Chlamydomonas will be investigated with particular emphasis on the flagellar proteins which require synthesis during regeneration and which can limit, therefore, flagellar growth. The flagella have been fractionated into microtubules and membranes. The membranes are being used to study the role of the membrane surface material in the cell - cell interaction which occurs during mating in Chlamydomonas. The mating is initiated in gametes by the agglutination of the flagella of opposite mating types. The microtubules have been fractionated and studies are being carried out on their in vitro reassembly. We have been able to use flagellar microtubules as seeds for the in vitro assembly of chick brain neurotubules. Current studies are aimed at obtaining the in vitro assembly of flagellar microtubules in both mutant and wild-type cells. Other current studies on the in vitro assembly of microtubules concern the attachment of microtubules to other cell structures (chromosomes, centriolar satellites, centrioles, etc.), the role of small molecules in the control of microtubule assembly, and the directionality of microtubule growth in vitro.